1^4 THE GEOLOGY OF TASMANIA— THE PRE-CAMBRIAN. 



The same author has drawn attention to the exist- 

 ence of similar epochs of diastrophism in Asia, and cor- 

 relates the Asiatic succession with that of North America 

 by a time relation to these diastrophic epochs. 



AVith the question of the North American-Asiatic 

 correlation we are not here concerned ; but we are 

 bound to consider most carefully Professor Adams' 

 contention that the Pre-Cambrian group should be 

 divided into three systems rather than two. For Pro- 

 fessor Adams insists that the upper break — called by 

 Professor Lawson the " eparchaean interval " — is " one 

 of the greatest unconformities in the whole of the Pre- 

 Cambrian succession of Laurentia, and probably quite 

 as important, if not more so, than the break at the close 

 of the Keewatin " (i). 



As regards the Tasmanian Pre-Cambrian terrain, 

 any attempt to apply in detail the conclusions arrived at 

 by American geologists is not yet warranted. 



While close correlation cannot be attempted, some 

 account should be given of the more general relation- 

 ships of the Tasmanian occurrences. 



We know that the Pre-Cambrian rocks of Tasmania 

 are typically such as would be designated Algonkian by 

 Van Hise. Moreover, the writer holds the opinion that 

 there is, at least in the district surrounding the head of 

 the Jane River, a twofold division of these rocks, and 

 that the two groups are separated b)^ an unconformity. 

 But much detailed field work must yet be done before 

 any sound deductions can be drawn from the existence 

 of this unconformity. Exact correlation with the rocks 

 of distant geological provinces is quite impossible. 



Moreover, it must be borne in mind that one uncon- 

 formity only has yet been observed in the Tasmanian 

 Pre-Cambrian development. In the North American 

 succession three unconformities above the Lower 

 Huronian series (2) are recognised by the members of 

 the classification committee, although there is a want of 

 agreement in the matter of the importance that should 

 be attached to the different unconformities. On this 

 question the special committee expressed no opinion. 



(i) Loc. cit., p. 122. 



(2) See comparative table at the end of this paper. 



